1. Field of the Invention
This invention relates to a technique for recording an information onto an optical disc in which a support signal indicating the physical position of a signal track is preformatted on an area different from the signal track, and more particularly to an optical disc recording method which records an information onto an discontinuous recording position of the signal track and an apparatus thereof.
2. Description of the Prior Art
In the conventional optical disc, such as a compact disc, hereinafter referred simply to as "CD", and a digital versatile disc, hereinafter referred simply to as "DVD", a signal track on which an information is to be recorded is formed in the spiral or concentric shape. Also, in the optical disc, a support signal is preformatted such that the signal track can be accessed in a random basis. This support signal divides the signal track into unit storage areas having a constant size and indicates the physical position of these unit storage areas.
The support signal has been preformatted on the optical disc in the two methods, that is, in the hard sector system and the soft sector system. According to the former hard sector system, the support signal is preformatted on the optical disc by defining embossed pits in the partial area of the signal track of the optical disc. In an optical disc in which the support signal is preformatted in this way, as shown in FIG. 1, signal tracks in the concentric or spiral shape are divided into a constant size of sectors 14. Each of these sectors 14 consists of a sector identification signal portion 16 and a main information signal portion 18. The sector identification signal portion 16 includes a synchronous pattern, an address mark, a track number and a sector number, thereby to indicate a boundary portion with adjacent sectors and to be used as a support signal indicating the physical position of that sector. The support signal in such a hard sector system occupies a partial region of the signal track on which user information is otherwise recorded. This results in a recording capacity of the optical disc being reduced.
On the other hand, the support signal in the latter soft sector system is positioned within a separate area that different from the signal track of the optical area, that is, a so-called wobbled area, so that it is possible to make a recording capacity of the optical disc large. In an optical disc in which the support signal is preformatted in this soft sector system, as shown in FIG. 2, wobbled grooves 22 defined from the center to the circumference of the optical disc in the spiral or concentric shape, hereinafter referred to as "groove tracks", are wobbled in a certain period, and lands 20, hereinafter referred to as "land tracks", are arranged in parallel with the groove tracks 22 between the groove tracks 22. The support signal is preformatted on the wobbled portion in either side of the groove tracks, hereinafter referred to as "wobbled area".
A user information block recorded on the signal track of the optical disc in which the support signal in such a soft sector system is preformatted, consists of a user block identification portion and a user block information portion. This user block identification portion includes a synchronous pattern, an address mark, a track number and a block number, etc. similar to the support signal in the spare sector system. The user block identification portion configured in this way indicates the physical position of the signal track of the optical disc at the time of reproducing. Accordingly, the support signal in the soft sector system is mainly used in the case where the user information is recorded onto the optical disc.
Further, the support signal is preformatted on the optical disc in such a pattern that it is synchronized with a clock signal having a constant period, in order to represent a transfer rate of the user information, that is, the recording and reproducing speed. In other words, a constant period of clock signal is included in the support signal preformatted on the optical disc. Clock signals included in each of the user block identification portion and the sector identification signal portion in the hard sector system have the same period as bits of the user information while a clock signal included in the support signal in the soft sector system has a relatively large period compared with bits of the user information. That is to say, a reference clock signal included in the support signal in the soft sector system has a lower frequency in comparison to the user information bit. Owing to this, in the optical disc in which the support signal in the soft sector system is preformatted, the phase of the clock signal recorded on the signal track may be changed suddenly. If the phase of the clock signal is suddenly changed as mentioned above, then since a clock signal having a period different from bit of the user information is reproduced, a part of the user information blocks recorded on the signal track is not reproduced accurately. This phenomenon occurs at a recording position in the signal track of the optical disc recorded discontinuously, hereinafter referred to as "discontinuous recording position". Moreover, it occurs more frequently as the number of the information files recorded on the signal track of the optical disc increases. This discontinuous recording position appears in the case where the first information file is recorded in a range from the start position of the signal track to an optional position in the intermediate thereof and, after a certain time has lapsed, the second information file is recorded from the optional position, and in the case where a new information is overwritten to an optional position of the signal track on which an information was recorded.
In reality, as shown in FIG. 3, if the first user information was recorded in a region S1 (not shown) ranged from the left side of the signal track 20 or 22 of the optical disc to an optional point DCP and, after a certain time has lapsed, the second user information was recorded from the optional point DCP, that is, the discontinuous recording position, then the phase of a recording clock recorded on the signal track 20 or 22 becomes suddenly changed at the discontinuous recording position L.sub.t as shown at (A) of FIG. 4A. This results from the recording clock recorded on the signal track 20 or 22 of the optical disc being generated on the basis of a reference clock signal included in the support signal in the soft sector system. This recording clock is reproduced by the optical disc reproducing apparatus such that it has a long period during the time interval extending to a predetermined region from the discontinuous recording position DCP, as shown at (B) of FIG. 4B, or such that it has a short period during the time interval extending to a predetermined region from the discontinuous recording position DCP, as shown at (C) of FIG. 4C. As described above, since the recording clock signal recorded in a predetermined region from the discontinuous recording position DCP of the signal track 20 or 22 is reproduced to have a long or short period, the user information recorded in that region is not recorded accurately.
In order to prevent such an error in the user information at the discontinuous recording position of the signal track of the optical disc, there has been suggested an alternative which adds clock stabilization information which is referred to as "variable frequency oscillating signal", hereinafter abbreviated to "VFO signal", to the discontinuous recording position. This clock stabilization information, however, is usually recorded over a single sector region from the discontinuous recording position, thereby causing a waste in the signal track of the optical disc unnecessarily. As a result, the above method of adding the clock stabilization information has a disadvantage in that it reduces the recording capacity of the optical disc considerably as the number of discontinuous recording positions in the signal track of the optical disc increases.